Getting too much caffeine can make you jittery, give you a headache and make it hard for you to fall asleep. The only way to totally get rid of the effects excessive caffeine can have on your body is to wait until it works its way out of your system in about four to six hours. However, you may be able to limit some of these effects by drinking water or tea and meditating.
Effects of Water
Caffeine can act as a diuretic, especially if you get a lot more than you're used to and from sources other than beverages. This could make you a little dehydrated and lead to a headache. In this case, drinking water might help you get rid of your headache and any other dehydration symptoms you're experiencing. However, drinking a large amount of water doesn't flush the caffeine out of your system.
Forget the Banana
Although some people recommend a banana for counteracting the effects of caffeine, the science just doesn't back this up, according to Dr. Randy Eichner in a March 2013 article published on the NPR website. The idea is that caffeine makes you dehydrated and low in potassium, so the potassium in the banana will help remedy the symptoms you're experiencing. You'd have to get a very large dose of caffeine for it to have an effect on your potassium levels and, even then, one banana doesn't have enough potassium to make much of a difference in your potassium levels.
Preliminary research suggests that a chemical in tea, called L-theanine, may help counteract some of the issues with sleep caused by overconsuming caffeine. A study using rats published in "Pharmacology, Biochemistry and Behavior" in April 2012 found that L-theanine may help decrease disturbances in short-wave sleep due to caffeine. Further studies are necessary to see if this chemical helps people as well as animals and what dose would be necessary. In the meantime, it wouldn't hurt to drink a cup of decaffeinated tea.
Being still and participating in activities like meditation and yoga may help you calm down and get over that jittery feeling from too much caffeine. Both of these activities help with relaxation. Meditation may also decrease your heartbeat and blood pressure, both of which can be affected by excessive caffeine consumption.